1. Technical Field of the Invention
The present invention relates to methods of manufacturing a ceramic sheet and, more particularly, to a method of manufacturing a ceramic sheet for use in a gas sensing element or the like.
2. Description of the Related Art
In the related art, an attempt has heretofore been made to provide
An attempt has heretofore been made to provide a method of manufacturing a stacked type gas sensing element for detecting a specified gas concentration in measuring gases in a manner as shown in FIG. 10A typically showing the related art disclosed in, for instance, Japanese Patent Application Publication No. 2002-286680.
As shown in FIG. 10A, raw materials are prepared using a ceramic powder, a binder 912, and a plasticizer 913 and mixed. The resulting mixture is then formed into unfired green sheets 90. Subsequently, an electrically conductive paste is printed on a surface 900 of each unfired green sheet 90 in one areas forming an electrode pattern and a heating pattern or the like. In addition, a ceramic insulating paste is printed on the surface 900 of the unfired green sheet 90 in the other areas thereof with no formation of the electrode pattern and the heating pattern in a reversed pattern opposite to the electrically conductive pattern. Then, a plurality of unfired green sheets 90, subjected to the printing processes mentioned above, are stacked to form a stacked ceramic body. Thereafter, the stacked ceramic body is fired, thereby obtaining a gas sensing element composed of the ceramic sheets in a stacked structure.
In recent years, the stacked type gas sensing eminent has been formed in a complicated structure. In a manufacturing process of such a stacked type gas sensing element, the number of times for the paste to be printed on the surface 900 of the unfired green sheet 90 has been increasing with an increase in the number of unfired green sheets 90 to be stacked. Therefore, the number of times for the unfired green sheet 90 to be dried after the paste has been printed has been increasing with the resultant consequence of a progressive increase in deformation of the unfired green sheet 90 during drying stages. That is, as the paste is printed on the unfired green sheet 90, the wetting and contraction occur on the unfired green sheet 90, causing a change to occur in dimension of the unfired green sheet 90 in a dried state.
Such a tendency seems to occur because of the reasons listed below.
That is, when the paste is printed on the unfired green sheet 90, the solvent present in the paste penetrates the unfired green sheet 90. This causes the solvent to dissolve the binder 912 contained in the unfired green sheet 90. Thus, ceramic particles 911 present in the ceramic powder move with respect to each other in a rearranged state, as shown in FIG. 10B, under which the unfired green sheet 90 is dried. As a result, the dimension of the unfired green sheet 90 is conceived to change after the drying step as shown in FIG. 10B.
To address such an issue, a measure has been taken in the related art to execute a method of selecting a solvent that is hard to cause the wetting and contraction of the unfired green sheet 90.
However, with such a method, there is a fear of a drop occurring in a thermal compression force between the unfired green sheets 90 with the resultant degradation in a bonding capability.